Threaded fasteners such as screws or bolts usually require a tool such as a screwdriver or wrench to be tightened or loosened. When a threaded fastener is employed in an assembly where it is assembled and disassembled frequently, it is frequently made with a self tool. The most familiar self tool for a threaded fastener is a wing nut and it is characterized by having a threaded central area capable of receiving a bolt and two wing elements that extend far enough from the central threaded area to provide a means to grasp the nut with the fingers and enough leverage to tighten or loosen it by hand.
Most threaded fasteners having self tools are cumbersome and to some extent interfere with utility. For example, a wing nut employed with a hand tool or a rotating device presents at minimum an uncomfortable projection from the tool and frequently a dangerous, threatening surface or projection from it. A typical example of the above is a knife with a replaceable blade having a handle that is held together with a threaded fastener. Blades are replaced by separating the handle into two halves, removing the old blade from between them and inserting a new one after which the two halves are firmly held together with the blade between them by tightening the threaded fastener.
Knives of this character usually require a tool such as a screwdriver to tighten or remove the threaded fastener. Sometimes the slot in the head of the threaded fastener is wide enough to receive a large coin which provides a good enough grip and enough leverage to loosen and tighten the fastener. But whether a screwdriver or a large coin is employed some type of tool must be used.
When a knife with a replaceable blade is used by a professional such as a carpet layer or a wall board installer, blades in a replaceable blade knife must be replaced frequently. When a tool is needed to separate and reassemble such a knife it is inconvenient and time-consuming. For such knives a self tool is desired on the threaded fastener. However, the available self tool fasteners reduce the utility by interfering with the hand grip or catching on the material being worked on, for example, the nap of a shag rug.